Free A/B test calculator
Did version B really win, or did it get lucky?
Your test data
Version A (control)
Version B (variant)
Confidence level
95% is the usual choice. Higher confidence needs more visitors.
Result
Yes. The difference is significant at 95% confidence.
p-value 0.0355. B converts better than A.
A converts at
10.00%
B converts at
13.00%
Lift of B over A
+30.0%
Likely real difference: +0.21 to +5.79 percentage points (95% range).
Low power. More visitors would make the answer more reliable.
Visitors needed per version
1,774
To detect a gap this size at 95% confidence with 80% power.
Uses a two-sided two-proportion z-test on your numbers. The p-value uses the pooled conversion rate; the range and power use each version's own rate. Visitors needed assumes 80% power and the gap you see now. It is a guide for your decision, not a guarantee of future results.
How to read it
Three numbers decide the call.
01
The p-value
How likely a gap this big would be if A and B truly performed the same. Below 0.05 means significant at 95% confidence.
02
The confidence range
The likely size of the real difference, in percentage points. If the range crosses zero, B might not be better at all.
03
Visitors needed
How many visitors each version needs to reliably detect a gap this size. Decide it up front and do not stop the test early.
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